[PATCH v3 16/23] Documentation: userspace-api: iommufd: Update vQUEUE

Nicolin Chen
2025-05-02T00:15:07Z

With the introduction of the new object and its infrastructure, update the
doc to reflect that.

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
Documentation/userspace-api/iommufd.rst | 15 +++++++++++++++
1 file changed, 15 insertions(+)

diff --git a/Documentation/userspace-api/iommufd.rst b/Documentation/userspace-api/iommufd.rst
index b0df15865dec..ed32713a97a3 100644
--- a/Documentation/userspace-api/iommufd.rst
+++ b/Documentation/userspace-api/iommufd.rst
@@ -124,6 +124,20 @@ Following IOMMUFD objects are exposed to userspace:
used to allocate a vEVENTQ. Each vIOMMU can support multiple types of vEVENTS,
but is confined to one vEVENTQ per vEVENTQ type.

+- IOMMUFD_OBJ_VQUEUE, representing a hardware accelerated virtual queue, as a
+ subset of IOMMU's virtualization features, for the IOMMU HW to directly read
+ or write the virtual queue memory owned by a guest OS. This HW-acceleration
+ allows VM to work with the IOMMU HW directly without a VM Exit, i.e. reducing
+ overhead from the hypercalls. Along with this vQUEUE object, iommufd provides
+ user space an mmap interface for VMM to mmap a physical MMIO region from the
+ host physical address space to the guest physical address space, allowing the
+ guest OS to control the allocated vQUEUE HW. Thus, when allocating a vQUEUE,
+ the VMM must request a pair of VMA info (vm_pgoff/size) for an mmap syscall.
+ The length argument of an mmap syscall can be smaller than the given size for
+ a partial mmap, but the addr argument of the mmap syscall should never offset
+ from the returned vm_pgoff, which implies that an mmap will always start from
+ the beginning of the physical MMIO region.
+
All user-visible objects are destroyed via the IOMMU_DESTROY uAPI.

The diagrams below show relationships between user-visible objects and kernel
@@ -270,6 +284,7 @@ User visible objects are backed by following datastructures:
- iommufd_viommu for IOMMUFD_OBJ_VIOMMU.
- iommufd_vdevice for IOMMUFD_OBJ_VDEVICE.
- iommufd_veventq for IOMMUFD_OBJ_VEVENTQ.
+- iommufd_vqueue for IOMMUFD_OBJ_VQUEUE.

Several terminologies when looking at these datastructures:

--
2.43.0